1. Field of the Invention
This invention relates to apparatus and methods for securing foundation anchors to foundations. More particularly, this invention relates to foundation anchors which are embedded in the ground for the purpose of resisting earth pressure and hydraulic pressure acting on concrete structures, and resisting the floating-up tendency of structures due to the buoyancy effect of underground water.
2. Description of the Prior Art
Prior art foundation anchors are known which comprise elongated steel rods, bars, strands, and/or wire, either separately or in bundles. These anchors are used to resist pressures to which concrete foundations are normally subjected, such as the lateral thrust of earthen backfill and hydraulic pressures. Hydraulic pressures may be either lateral, against the foundation side wall, or buoyantly vertical, caused by water beneath the foundation.
The anchors are customarily anchored in the earth by some form of deadman, sometimes secured in a bed of grout. Various conventional means are known for fastening and tensioning anchors to foundation walls. These means are divided broadly into two groups consisting of wedge fasteners and threaded fasteners. This invention is solely concerned with anchors in the threaded fastener group. Threaded fasteners are advantageous over wedges in that threaded fasteners are more reliably secured and are less likely to permit a loss of tension in the anchor.
A threaded fastener comprising a threaded shank on the rod, bar, or strand anchor tension member and a nut threaded on the shank is usually employed in conjunction with a bearing plate on the side of the foundation wall opposite the anchor. A hole in the foundation and in the bearing plate permits the threaded shank of the anchor tension member to pass through the foundation wall. A nut is then threaded onto the shank and brought into pressure engagement with the bearing plate, which pressure also tensions the anchor tension member.
The disadvantage of the threaded fastener type anchor tension member is that the surface area on the bearing plate required to turn the nut severely limits the number of nuts that can be accommodated on a bearing plate without resorting to a bearing plate which is impractically excessive in area. In the alternative, to bridle a plurality of anchor tension members to a single threaded shank tends to overload and thereby strip the threads of the nut, thus losing the tension in the bridled tension members. As a consequence, when a plurality of tension members are fastened to one bearing plate, the wedge securing and fastening system is the apparatus and method most commonly used.